(a) Field of the Invention
This invention relates to vibrator devices of the type which produce a vibratory effect as a result of rotation of an out-of-balance mass. It is of particular, but by no means exclusive, application to vibratory surface compactors and especially vibratory road rollers.
(b) Description of the Prior Art
Devices of the type concerned normally employ a mechanically unbalanced rotor on rotation of which the resultant vibratory force is transmitted to the body being vibrated through the rotor shaft and the bearings thereof. Vibratory road rollers are now in common use, the drum of such a roller being vibrated to increase the ground compacting effect several times as compared with that of a dead-weight roller of the same weight. Conventional vibratory rollers employ a system of eccentric weights mounted within the drum on a high-speed spindle which passes through the drum coaxially thereof and which is coupled externally to a separate vibrator engine.
The eccentric weights revolve at high speed to produce the high centrifugal vibratory forces and vibratory frequency required to compact the surface being rolled. These high frequency forces are transmitted to the drum through the spindle bearings of the roller and on large machines the centrifugal forces and the inertia of the eccentric weights and associated mechanism imposes very high stresses of an unfavourable nature on the bearings and the control and drive mechanism, necessitating a heavy and expensive construction.
The bearings are accordingly costly and they moreover tend to have a short life. A further disadvantage is that the spindle must be accelerated rapidly up to a high speed at the start of a rolling operation, and decelerated rapidly at the end thereof as vibration of the drum with the roller stationary would produce unacceptable ground indentation. Thus a large vibrator engine is required, particularly in relation to the normal power output required, and complex drive and brake arrangements are required which are also subject to rapid wear.